A cold pilger rolling mill has at least one roll stand that is reciprocated horizontally by a crank drive comprising a crank arm with a counterweight for at least partially counterbalancing the mass forces generated by the roll stand. A connecting rod is pivoted on and connects the roll stand and the crank arm to one another.
A drive system of this type is known, for example, from U.S. Pat. No. 5,540,076. In order to carry out the cold pilger process, a roll stand is equipped with a cold pilger roll pair that is driven reciprocated, normally horizontally. To this end, a crank drive is used that is driven by a motor. The crank drive is provided with a counterweight in order to balance the mass forces of the roll stand with a counterweight. However, this weight is usually not enough to provide sufficient balance for the mass forces.
The productivity of a cold pilger mill is a direct function of the stroke rate of the roll stand per time unit, for which reason the greatest possible number of working strokes per minute is desired for reasons of cost effectiveness. However, this also leads to large mass forces that subject the drive system and particularly its bearing as well as the base and therefore the surroundings to a considerable load. Therefore, in the solution mentioned above, provision is made for the crank drive to drive an additional shaft on which a counterweight is eccentrically connected relative to the center of gravity via a gearing. This counterweight rotates in the opposite direction when the crank drive rotates and is thus able to generate equalizing mass forces and/or mass momentums such that an equalization of mass force results overall in the entire drive system.
In this known embodiment, it is disadvantageous that the entire drive system is quite expensive and complex because a large number of machine elements—engaged in one another via gears—are necessary. This also increases the cost of the drive system and therefore of the cold pilger mill; the increased costs include not only the investment costs for the system itself, but also costs for the system base, for replacement and expendable parts, as well as costs for maintenance and repair.
From DE 962 062 a drive system is known for a cold pilger mill in which the crank arm is equipped for driving the roll stand with flyweights and a vertically oscillating counterweight for equalizing the mass forces of the first order as well as the mass momentums in the drive. This solution has the disadvantage that the base of the roll mill has a very complex and therefore expensive structure because provision must be made for the counterweight to vertically plunge into the base. A large and deep cellar is required for this purpose, which correspondingly increases the costs for the roll mill.
U.S. Pat. No. 5,076,088 discloses a drive for the roll stand of a cold pilger mill, with a planetary crank drive being used for driving and equalization of mass forces and mass momentums. Although this solution is able to provide an optimal mass equalization, this drive is only suitable for smaller cold pilger mills because, for larger systems, the overall size of such a drive system would increase disproportionally and thus incur high costs.
U.S. Pat. No. 7,082,799 describes a drive system for a cold pilger mill that uses, in order to improve the mass force equalization, separate shafts with counterweights, these shafts being driven by a drive that is independent of the drive of the crank drive. The synchronization of the drives when the roll mill is in operation is performed electronically. However, the expense required for this system is not insignificant.
Therefore, in known drive systems for cold pilger mills, double-offset, expensive crank shafts are used that move the roll stand in an oscillating fashion via connecting rods. The counterweights on the crank shaft and on additional rotating auxiliary shafts eliminate the mass forces that ensue due to the back-and-forth movement of the roll stand.